The use of nanoparticles in the form of metal nanoclusters in biotech applications is known in the art. US2010029016, for instance, describes a composition which is capable of being used for detection, comprising an encapsulated noble metal nanocluster. Methods for preparing the encapsulated noble metal nanoclusters, and methods of using the encapsulated noble metal nanoclusters are also described. The noble metal nanoclusters are preferably encapsulated by a dendrimer or a peptide. The encapsulated noble metal nanoclusters have a characteristic spectral emission. The spectral emission is varied by controlling the nature of the encapsulating material, such as by controlling the size of the nanocluster and/or the generation of the dendrimer. The emission is used to provide information about a biological state.